Magnetic tape cassette

ABSTRACT

The present invention aims to prevent damages of a magnetic tape in a magnetic tape cassette adapted to be operated in a recording and reproducing apparatus which can similarly operate a plurality of magnetic tape cassettes. 
     More specifically, in the invention, differences (A 1 −B 1 , A 2 −B 2 ) between heights A 1 , A 2  of radially inner portions ( 32   a ), ( 42   a ) of lower flanges ( 32 ), ( 42 ) and heights B 1 , B 2  of ribs ( 35   a ), ( 45   a ) of lower halves ( 35 ), ( 45 ) for restricting a height of the magnetic tape are equal (A 1 −B 1 =A 2 −B 2 ) in a plurality of the magnetic tape cassettes which have the same vertical sizes and different sizes in a horizontal direction.

TECHNICAL FIELD

The present invention relates to a magnetic tape cassette such as adigital video cassette (DVC) and so on.

BACKGROUND OF THE INVENTION

As a magnetic recording medium, there has been a magnetic tape cassettehaving a pair of tape reels, around which a magnetic tape is wound andwhich is rotatably contained in a cassette case. FIG. 10 is an explodedperspective view of a magnetic tape cassette for a DVC (a digital videocassette) as one example of the magnetic tape cassettes of this type.

As shown in FIG. 10, a cassette case of this magnetic tape cassette 50is composed of an upper cassette half (hereinafter referred to as anupper half) 51 in a substantially rectangular shape, and a lowercassette half (hereinafter referred to as a lower half) 52. The lowerhalf 52 is formed, at its center part, with two reel holding holes 53 a,53 b, and at its front face with a space 54 for inserting a tapewithdrawing member which is provided on a recording and reproducingapparatus.

Also, at the front face of the lower half 52, there is formed a lowerhalf portion 55 a of a front wall 55 which defines this space 54, and atboth sides of the space 54, there are respectively formed cut-outs 57 a,57 b for introducing a magnetic tape 56 to the exterior and to theinterior. There are further provided tape guides 58 a, 58 b respectivelybetween ends of the lower half portion 55 a of the front wall 55 and thecut-outs 57 a, 57 b. On the other hand, the upper half 51 is alsoprovided, at its front face, with an upper half portion 55 b of thefront wall 55 which defines the space 54 for inserting the tapewithdrawing member which is provided on the recording and reproducingdevice.

To the cassette case composed of the above described upper and lowerhalves 51, 52, is assembled an openable lid 60 so as to cover themagnetic tape 56 which is stretched across the above described space 54,in other words, exposed to the exterior from the cassette case, on suchoccasion as this cassette case is carried. This openable lid 60 iscomposed of three lids, namely, an outer lid (a front lid) 61, a top lid(an upper lid) 62, and an inner lid (a rear lid) 63.

Tape reels 70, 80 around which the magnetic tape 56 is wound arecontained in the above described cassette case so as to rotate in astate where they are respectively inserted in the above described reelholding holes 53 a, 53 b. These tape reels 70, 80 are composed of upperflanges 71, 81 and lower flanges 72, 82 restricting vertical movementsof the magnetic tape 56, and bosses 73, 83 which are integrally formedwith the lower flanges 72, 82 and around which the magnetic tape 56 iswound.

FIG. 11 is an enlarged view of an area surrounding the tape guide 58 a.As shown in FIG. 11, the tape guide 58 a which is formed between the endof the lower half 55 a of the front wall 55 and the cut-out 57 a guidesthe magnetic tape 56. This magnetic tape 56 is wound around the bosses73, 83 of the magnetic tape reels 70, 80 as described above. When theopenable lid 60 is closed, that is, when the magnetic tape 56 is notrunning for play back or so, positioning of the magnetic tape 56 in avertical direction is conducted by means of the lower flanges 72, 82 andribs 59 a, 59 b which are formed at the front end of the above describedlower half 52.

By the way, there exist several magnetic tape cassettes having the abovedescribed structure, whose cassette cases are the same in height (sizein a vertical direction) and different in size in a horizontaldirection. More specifically, in such magnetic tape cassettes, diametersof the tape reels are made different in order to vary winding amounts ofthe magnetic tapes (duration of recording time), and the tape reels arerespectively contained in the cassette cases which are different in sizeonly in a horizontal direction. In order to deal with the magnetic tapecassettes which are different in size in this manner, there aredisclosed for example, in registered Japanese Patents Nos. 2636825,2636826 and so on, such recording and reproducing apparatuses which arecapable of operating a plurality of the magnetic tape cassettes in thesame manner.

Conventionally, as the magnetic tape cassettes to be loaded in such arecording and reproducing apparatus, there have been a large cassettehaving a relatively long recording time (hereinafter referred to simplyas “an L cassette”), a small cassette having a relatively shortrecording time (hereinafter referred to simply as “an S cassette”), anda cassette having a medium recording time (hereinafter referred tosimply as “an M cassette”). However, they are not so different in size.Therefore, even though a thickness of the cassette case of the Lcassette is the same as a thickness of the cassette case of the Scassette, there has been no problem in the L cassette with respect tostrength.

In recent years, there has been an increasing need for using a furtherlarger cassette than the above described L cassette (hereinafterreferred to simply as “an LL cassette”) for the purpose of furtherincreasing the recording time. However, provided that a height of the LLcassette should be maintained to be the same as the height of the abovedescribed S and L cassettes while a thickness of the LL cassette ismaintained to be equal to the thickness of the other cassettes, therewill be arisen such a problem that a flexure may occur in the cassettecase, in other words, a problem of strength, because the LL cassette hasa larger area in a horizontal direction. For this reason, it isnecessary to take such a countermeasure for the LL cassette that thethickness of the cassette case is increased. In this case, if it isintended to ensure an increased amount in size of the thickness of thecassette case by varying the height of the LL cassette, the recordingand reproducing apparatus must be inevitably upsized correspondingly,and a problem of an increased cost may be concerned. From thisviewpoint, it has been considered that the vertical size of the LLcassette had better be maintained at the same size as it currentlystands.

However, when the strength of the cassette case is intended to beensured by increasing the thickness of the LL cassette without changingthe vertical size of the LL cassette, gaps inside the LL cassette willbecome narrow. On the other hand, because the tape reels are suchmembers as rotating inside the cassette case when driven, the gaps of acertain extent must be maintained between the cassette case and the tapereels so that the rotation may not be hindered.

Therefore, in order to obtain the predetermined gaps between thecassette case and the tape reels, such a method has been considered thata distance between the upper and the lower flanges composing the tapereels may be reduced to such an extent that a lateral size of themagnetic tape may not be interfered, in other words, the lower flangesmay be positioned at a higher level and the upper flanges may bepositioned at a lower level than in the S cassette and the L cassette.However, as described above, positioning of the magnetic tape cassettein the vertical direction is conducted by means of the lower flanges andthe ribs provided at the front end of the lower half. For this reason,by taking this countermeasure, a difference in height between portionswhere the magnetic tape starts to be wound (radially inner portions ofthe lower flanges) and tape withdrawing portions (the aforesaid ribs ofthe lower half) will be too large in the LL cassette. As a result, thetape may be, so to say, slackened when the openable lid is closed, andthere has been such probability that edges of the tape may be damaged.

FIG. 12 is a plan view of the lower half 52 of the DVC, in which (a)shows the lower half 52 of the DVC of the M cassette and (b) shows thatof the L cassette. A distance between the positioning holes 90 a, 90 bfor positioning them when loaded in the recording and reproducingapparatus, as well as a distance between a pair of the tape guides 58 a,58 b provided in forward parts of the cassette are the same both in theM cassette and the L cassette. This is because a recording andreproducing head, tape guide pins, and so on can be co-used with boththe cassettes in the recording and reproducing apparatus.

Here in the drawings, hatched areas are tape running areas S in therecording and reproducing apparatus. The L cassette is larger than the Mcassette in an outer shape, while distances between the tape guides 58 aand 58 b are equal in both the cassettes. Bosses 91 a, 91 b for smallscrews cooperate with the tape guides 58 a, 58 b to define tape runningopenings 92. A width of the tape running opening 92 in the L cassette islarger than that of the tape running opening 92 in the M cassette.

Accordingly, the tape running areas S of the L cassette are larger inwidth than the tape running areas S of the M cassette in the recordingand reproducing apparatus. For this reason, no additional member can beprovided in areas corresponding to the tape running areas S of the Lcassette in the recording and reproducing apparatus, and so, aneffective use of an interior of the recording and reproducing apparatusis impossible.

Moreover, in case where it has become necessary to mount an additionalmember near the opening of the cassette in the recording and reproducingapparatus, the member must be mounted avoiding the tape running areas Sof the L cassette. This will incur upsizing of the recording andreproducing apparatus.

Further, the magnetic tape cassettes are classified into those forpersonal use and those for business use according to their applications.FIG. 13 is an exploded perspective view showing main components of abeta cam L cassette which is a magnetic tape cassette for business use.

As shown in FIG. 13, this beta cam L cassette 220 is substantiallycomposed of an upper half 224 and a lower half 222 constituting acassette case, a pair of pay-off and take-up tape reels 228, 230 whichare rotatably contained in the upper and lower halves 224, 222 and havea magnetic tape 226 wound around, and a lid 232 for covering frontopenings of the upper and lower halves 224, 222 so as to be opened andclosed.

In addition to the above, there are provided a plurality of small screws234 for joining the upper and lower halves 224, 222 with each other, apair of guide rollers 236 and a pair of guide pins 238 made of metalwhich are arranged at tape pay-off and take-up openings in the lowerhalf 222, and so on. Further, in the drawing, reference numeral 246represents reel holders arranged on the tape reels 228, 230, referencenumeral 248 represents reel springs for biasing the tape reels 228, 230via the reel holders 246, and reference numeral 250 represents centercaps for locking the reel springs 248 from above the upper half 224.

Pads 244 press the magnetic tape 228 with appropriate biasing force byslidably contacting their side faces with a back face of a magnetic tape228 which passes between the guide rollers 236 and the guide pins 238 atthe opening end. A magnetic tape 226 taken out from the cassette 220 isguided by means of a variety of guide pins, which are not shown, in therecording and reproducing apparatus, wound around a head which is notshown, and then, paid off or taken up according to rotation of a capstanmotor.

Among the above described various components, the guide rollers 236 areformed of resin molded articles such as POM, for example, which hassmoothness and mechanical strength. Moreover, each of the guide rollers236 is formed in a barrel-like shape in its exterior, as shown in FIG.14, for the purpose of ensuring safe running of the magnetic tape 226and guiding it effectively, and supported so as to rotate by idlyengaging its center hole 236 a with a bearing pin which is projectedfrom the lower half 224.

Generally, on occasion of injection molding of such a molded article, aparting line PL between molds is positioned on an end face of the moldedarticle as shown in FIG. 14. As a result, when it is molded into abarrel-like shape, a larger diameter portion swelling at the middle ismade undercut, and the article cannot be extracted in case where it hasa larger swelling amount than a certain value. Therefore, it has beenusually formed into the barrel-like shape through a cutting work bymachine from a rod-like material.

However, in case where the cutting work by machine has been employed,there has been such a problem that cutting amount has been large at boththe ends, requiring a lot of working time. In addition, because the workrequires an expensive machine such as an NC lathe, a cutting cost wouldbe extraordinary high.

DISCLOSURE OF THE INVENTION

The present invention has been made in view of the above describedcircumstances, and its object is to prevent damages of a magnetic tapein a magnetic tape cassette to be operated in a recording andreproducing apparatus which can operate a plurality of magnetic tapecassettes in the same manner.

It is another object of the invention to provide a magnetic tapecassette capable of conducting recording and reproducing of cassetteshaving a plurality of sizes, without upsizing the recording andreproducing apparatus.

It is a further object of the invention to provide a process forproducing a guide roller in a magnetic tape cassette, which can bedirectly molded into a barrel-like shape by injection molding, whosesubsequent work is simple, and which can be manufactured at a low cost.

A first invention is to provide a magnetic tape cassette adapted to beoperated in a recording and reproducing apparatus which can similarlyoperate a plurality of magnetic tape cassettes having the same verticalsize and different sizes in a horizontal direction,

-   -   each of the plurality of the magnetic tape cassettes being        provided with tape reels having upper and lower flanges for        restricting vertical movements of a magnetic tape and bosses        around which the magnetic tape is wound, and a cassette case        consisting of an upper and a lower halves for rotatably        containing the tape reels, the magnetic tape being restricted in        height by means of the lower flanges and ribs provided at a        front end of the lower half, and    -   further, radially inner portions of the lower flanges of the        tape reels in the plurality of the magnetic tape cassettes being        respectively set to have different heights,    -   characterized in that differences between the heights of the        radially inner portions of the lower flanges and the heights of        the ribs in the lower halves for restricting the height of the        magnetic tape are the same in the plurality of the magnetic tape        cassettes.

According to the magnetic tape cassette of the first invention, providedthat the height of the radially inner portion of the lower flanges whichare portions where the magnetic tape starts to be wound is A, and theheight of the ribs in the lower half which are withdrawing portions ofthe magnetic tape is B, the difference (A−B) is the same in the magnetictape cassettes having different sizes (for example, the S cassette, theL cassette, and the LL cassette). Because the difference in the partsfor restricting the height of the magnetic tape in the LL cassette isappropriately established in this manner, a certain amount of tensioncan be obtained.

Accordingly, even in a large cassette, positional restriction of themagnetic tape can be conducted in a stable manner, and damage of thetape edges will be prevented.

A second invention is to provide a magnetic tape cassette characterizedin that in a plurality of magnetic tape cassettes which have differentouter sizes and are operable in a same recording and reproducingapparatus, distances between positioning marks are equal, that distancesbetween a pair of guide members for defining tape running areas of apair of tape running openings at inner sides of the cassettes aredifferent, and that tape running paths connecting bosses around whichmagnetic tapes are wound and the guide members have the sameinclinations.

According to the second invention, even in the plurality of the magnetictape cassettes which have different outer sizes, the tape running areaswill not be remarkably enlarged in the recording and reproducingapparatus, even though the outer sizes are increased, because the taperunning paths connecting the bosses around which the magnetic tapes arewound and the guide members have the same inclinations. As the results,it will be possible to provide additional members or the like near thetape running openings of the cassettes in the recording and reproducingapparatus. Thus, the recording and reproducing apparatus will not beupsized by providing the members.

Further, a third invention is to provide a magnetic tape cassettecharacterized in that in a plurality of magnetic tape cassettes whichhave different outer sizes and are operable in a same recording andreproducing apparatus, distances between positioning marks are equal,that widths of a pair of tape running openings in a horizontal directionof the cassettes are equal, and that distances between a pair of guidemembers for restricting tape running areas of the tape running openingsat inner sides of the cassettes are different.

According to the third invention, even in a plurality of the magnetictape cassettes which have different outer sizes, the tape running areaswill not be remarkably enlarged even though the outer sizes areincreased, because the widths of a pair of the tape running openings ina horizontal direction of the cassettes are equal. As the results, itwill be possible to provide additional members or the like near the taperunning openings of the cassettes in the recording and reproducingapparatus. Thus, the recording and reproducing apparatus will not beupsized by providing the members.

A fourth invention is to provide a process for producing guide rollersin a magnetic tape cassette, the guide rollers being rotatably supportednear an inlet and an outlet of a magnetic tape and adapted to guidepay-off and take-up of the magnetic tape,

-   -   characterized in that each of the guide rollers is a resin        molded article having its cylindrical part in a barrel-like        shape, and that a parting line between molds for injection        molding is positioned at the largest diameter portion of the        guide roller to mold it into a barrel-like shape, and        thereafter, a molding burr projected from the parting line is        removed.

A fifth invention is to provide a process for producing guide rollers ina magnetic tape cassette, the guide rollers being rotatably supportednear an inlet and an outlet of a magnetic tape and adapted to guidepay-off and take-up of the magnetic tape,

-   -   characterized in that each of the guide rollers is a resin        molded article having its cylindrical part in a barrel-like        shape, and that a parting line between molds for injection        molding is positioned at both ends of the guide roller to mold        it into a barrel-like shape, and thereafter, a molding burr        projected from the parting line is removed.

According to the production process of the above described fourthinvention, as a first step, the parting line between the molds forinjection molding is positioned at the largest diameter portion, forexample in the center part of the guide roller in a barrel-like shape.By filling molten resin into cavities in this state and molding, theguide roller is molded into a barrel-like shape. Thereafter, the moldingburr projecting from the parting line is removed.

According to the production process of the above described fifthinvention, as a first step, the parting line between the molds forinjection molding is positioned at both the ends of the guide roller. Byfilling molten resin into cavities in this state and molding, the guideroller is molded into a barrel-like shape. Thereafter, the molding burrprojecting from the parting line is removed.

Accordingly, in the production processes of the fourth and fifthinventions, undercuts will not occur in molding the guide roller intothe barrel-like shape. In the subsequent process, the molding burrslightly projecting from an outer periphery of the product may be onlyremoved, and the subsequent process will be finished simply and in ashort time.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view showing relation between tape reels and alower half in a first embodiment of the invention (The lower half issimplified).

FIG. 2 is a sectional view of a cassette case and one of the tape reelscontained in the cassette case.

FIG. 3( a) is a sectional view of a cassette case of an L cassette andone of the tape reels contained in the cassette case, and FIG. 3( b) isa sectional view of a cassette case of an LL cassette and one of thetape reels contained in the cassette case.

FIG. 4 is a plan view of a lower half of a magnetic tape cassetteaccording to a second embodiment of the intention, in which (a) is thelower half of an M size, and (b) is that of an L size.

FIG. 5 is a plan view of a lower half of a magnetic tape cassetteaccording to a third embodiment of the intention, in which (a) is thelower half of an M size, and (b) is that of an L size.

FIG. 6 is a sectional view showing shapes of molds in a fourthembodiment of the invention.

FIG. 7 is a perspective view showing a finished state of a guide rollerwhich has been molded by employing the molds in FIG. 6.

FIG. 8 is a sectional view showing shapes of molds in a fifth embodimentof the invention.

FIG. 9 is a perspective view showing a finished state of a guide rollerwhich has been molded by employing the molds in FIG. 8.

FIG. 10 is an exploded perspective view showing a conventional magnetictape cassette for a DVC.

FIG. 11 is an enlarged perspective view showing a tape guide in FIG. 10.

FIGS. 12 (a) and 12 (b) are plan views of a lower half of theconventional magnetic tape cassette.

FIG. 13 is an exploded perspective view showing main components of abeta cam L cassette, one example to which the guide roller of theinvention is applied.

FIG. 14 is a longitudinally sectional view and an end view showing aconventional process for producing a guide roller in a barrel-likeshape.

BEST MODE FOR CARRYING OUT THE INVENTION

Herein below, a first embodiment of the invention will be described indetail referring to FIGS. 1 to 3. FIG. 1 is a perspective view showingrelation between tape reels and a lower half in a first embodiment ofthe invention (The lower half is simplified), FIG. 2 is a sectional viewof a cassette case and one of the tape reels contained in the cassettecase, and FIG. 3( a) is a sectional view of a cassette case of an Lcassette and one of the tape reels contained in the cassette case, andFIG. 3( b) is a sectional view of a cassette case of an LL cassette andone of the tape reels contained in the cassette case.

As shown in FIG. 1, a magnetic tape cassette 1 of the embodiment has apair of tape reels 20, 25 in a cassette case consisting of an upper anda lower halves. These tape reels 20, 25 respectively have upper flanges21, 26 in a substantially disc-like shape for restricting verticalmovements of a magnetic tape 6, lower flanges 22, 27, and bosses 23, 28which are integrally formed with the lower flanges 22, 27 and aroundwhich the aforesaid magnetic tape 6 is wound. The upper flanges 21, 26and the bosses 23, 28 of the tape reels 20, 25 are fixed by engagingweldable ribs formed on top ends of the bosses 23, 28, which are notshown, respectively with holes formed in the upper flanges 21, 26, whichare not shown, and by ultrasonic welding the aforesaid weldable ribs.

The lower half 12 constituting a half body of the aforesaid cassettecase is provided with a lower half 5 a of a front wall, cut-outs 7 a, 7b through which the magnetic tape 6 is guided in and out, and tapeguides 8 a, 8 b which are formed between ends of the lower half 5 a andthe cut-outs 7 a, 7 b. These tape guides 8 a, 8 b are adapted to comeinto a sliding contact with the magnetic tape 6 while the magnetic tapecassette 1 is played back or so, to guide the magnetic tape 6 under acertain tension. Positioning of this magnetic tape 6 in a verticaldirection is performed by means of the lower flanges 22, 27 and ribs 9a, 9 b which are formed at a front end of the lower half 12, while anopenable lid is closed, in other words, the magnetic tape 6 is notrunning for playback or so.

As shown in FIG. 2, a height of a radially inner portion 22 a of thelower flange 22 is set to be A. Here, the height A means a distance froma surface of the lower half 12 (a face in contact with a table) to theradially inner portion 22 a of the lower flange 22 (a rectilineardistance in parallel to an axis of rotation of the tape reel 20), whenthe magnetic tape cassette 1 is placed on the table, for example.

Moreover, a height of the rib 9 a of the lower half 12 which is awithdrawing portion of the magnetic tape 6 is set to be B. Here, theheight B means a distance from the surface of the lower half 12 (theface in contact with the table) to an upper end of the rib 9 a (arectilinear distance in pararell to the axis of rotation of the tapereel 20). Moreover, although there are shown only the tape reel 20 and ahalf of the lower half 12 in FIG. 2, the relation as described below isthe same with the other tape reel 25 and the other half of the lowerhalf.

A difference (A−B) between the height A of the radially inner portion 22a of the aforesaid lower flange 22 and the height B of the rib 9 a ofthe lower half 12 is set to be equal in a plurality of magnetic tapecassettes having different sizes, for example, the S cassette, Lcassette and LL cassette.

More specifically, when a height A1 of a radially inner portion 32 a ofa lower flange 32 provided in the L cassette as shown in FIG. 3( a) is10 mm, for example, and a height B1 of a rib 35 a of a lower half 35 is9 mm, for example, a height A2 of a radially inner portion 42 a of alower flange 42 provided in the LL cassette as shown in FIG. 3( b) isset to be 12 mm, for example, and a height B2 of a rib 45 a of a lowerhalf 45 is set to be 11 mm, for example. In short, A1−B1=A2−B2=1 mm,which is the same in the L cassette and the LL cassette. By setting thedifference in this manner, the difference in parts for restricting theheight of the magnetic tape in the LL cassette is not different from thedifference in the L cassette, and therefore, even in the LL cassette, acertain tension will be created so that the magnetic tape 6 may not beslackened, and positional restriction of the magnetic tape 6 can beperformed in a stable manner.

Moreover, in the L cassette and the LL cassette which have an equal sizein height, establishing a relation of H1=H2 in short, and have differentsizes in a horizontal direction, other dimensional relations arepreferably set to be as follows; ≈□.

Relation between a thickness U1 of an upper half 36 and a thickness U2of an upper half 46 is U1≈U2 (relation U1>U2 to an extremely smallextent is preferably established in order to enlarge a gap between atape reel 40 and the upper half 46 in the LL cassette), and relationbetween a thickness L1 of the lower half 35 and a thickness L2 of thelower half 45 is L1≈L2 (relation L1>L2 to an extremely small extent ispreferably established in order to enlarge a gap between the tape reel40 and the lower half 45 in the LL cassette). Relation between adistance C1 between the upper half 36 and an upper flange 31 and adistance C2 between the upper half 46 and an upper flange 41 is C1≈C2(relation C1>C2 to an extremely small extent is preferably establishedin order to enlarge a gap between the upper flange 41 and the upper half46 in the LL cassette), and relation between a distance D1 between thelower half 35 and the lower flange 32 and a distance D2 between thelower half 45 and the lower flange 42 is D1≈D2 (relation D1>D2 to anextremely small extent is preferably established in order to enlarge agap between the lower flange 42 and the lower half 45 in the LLcassette).

Usually, a tape supporting face of the lower flange has a gradienttoward an outer circumference of the lower flange, and an effect of thisgradient may be concerned. However, because the gradient is very small,and even though a diameter of the lower flange is relatively large, thegradient will be smaller correspondingly, as shown in FIGS. 3( a), (b),it will be sufficient only that the above mentioned relations betweenthe heights A1, A2 and the heights B1, B2 be established as above.

It is to be noted that the invention is not limited to the abovedescribed embodiment, but appropriate modifications and improvements arepossible. For example, it goes without saying that the invention can beapplied to other cassettes than the DVC.

Now, a second embodiment of the invention will be described in detail,referring to FIG. 4. FIG. 4 is a plan view of a lower half of a magnetictape cassette according to the second embodiment of the invention. Sincea basic structure of this second embodiment is the same as that of theconventional magnetic tape cassette as shown in FIG. 10, the samecomponents will be denoted with the same reference numerals, and theirexplanation will be omitted or simplified.

FIG. 4( a) is a lower half of an M cassette, and FIG. 4( b) is a lowerhalf of an L cassette which has a larger outer dimension than the Mcassette.

Tape reels 70, 80 of the L cassette are larger than tape reels 70, 80 ofthe M cassettes and can have a larger amount of a magnetic tape woundaround them than in the M cassette. A pair of positioning holes 90 a, 90b as targets for positioning the cassette in a recording and reproducingapparatus 200 are provided at a front side of a lower half 52 in each ofthe cassettes. Distances between the positioning holes are the same inthe cassettes of both the sizes, and common positioning pins 190 a, 190b in the recording and reproducing apparatus 200 are inserted into thepositioning holes 90 a, 90 b from below the cassette, thereby toposition the cassette.

A pair of tape guides 58 a, 58 b for restricting running areas of amagnetic tape inside the cassette are provided near the positioningholes 90 a, 90 b. The magnetic tape is adapted to be stretched acrossthe pair of the tape guides 58 a, 58 b when the cassette is not in use.A distance between the pair of the tape guides 58 a, 58 b is longer inthe L cassette than in the M cassette.

However, relations between bosses 73, 83 of the reels 70, 80 and thetape guides 58 a, 58 b are the same in the L cassette and the Mcassette, and tape running paths connecting the bosses 73, 83 and thetape guides 58 a, 58 b have the same inclinations θ with respect to adetermined direction in both the cassettes. In this embodiment, theinclinations θ with respect to a back and forth direction of thecassettes are the same in both the cassettes.

As the results, although a width of a tape running opening 92 is largerin the L cassette than in the M cassette, the difference is not so largeas in the conventional case. Similarly, with respect to tape runningareas S in the recording and reproducing apparatus, there is no such alarge difference between the L cassette and the M cassette, as in theconventional case. As apparent when FIG. 4( b) is compared with FIG. 12(b), the tape running areas S of the L cassette according to thisembodiment in the recording and reproducing apparatus is remarkablynarrower than the tape running areas S of the conventional L cassette inthe recording and reproducing apparatus.

Therefore, according to this second embodiment, even though the cassetteis larger in size, the tape running areas S in the recording andreproducing apparatus will not be increased to a large extent. Thus,spaces near the tape running openings 92 can be effectively utilized,such as arranging additional members near the tape running openings 92.

Now, a third embodiment of the invention will be described.

FIG. 5 is a plan view of a lower half of a magnetic tape cassette in thethird embodiment according to the invention. Since a basic structure ofthis third embodiment is the same as that of the above described secondembodiment, the same components will be denoted with the same referencenumerals and their explanation will be omitted or simplified.

FIG. 5( a) shows a lower half 52 of the M cassette, and FIG. 5( b) showsa lower half 52 of the L cassette.

A characteristic structure of this third embodiment is that widths W ofthe tape running openings 92 in a horizontal direction of the cassettesare equal irrespective of dimension of the cassettes. Inner sides of themagnetic tape running openings 92 are defined by the tape guides 58 a,58 b, and outer sides thereof are defined by bosses 91 a, 91 b for smallscrews. The distances W between the tape guides 58 a, 58 b and thebosses 91 a, 91 b for the small screws forming the tape running openings92 are equal in both the cassettes. Moreover, distances between thepositioning holes 90 a, 90 b are equal in both the cassettes, and adistance between the tape guides 58 a, 58 b in the L cassette is largerthan that in the M cassette.

Although the tape running areas S of the L cassette in the recording andreproducing apparatus is larger than those of the M cassette, there isnot such a large difference as in the conventional case. As is apparentwhen FIG. 5( b) is compared with FIG. 12( h), the tape running areas Sof the L cassette according to this embodiment in the recording andreproducing apparatus is remarkably narrower than the tape running areasS of the conventional L cassette in the recording and reproducingapparatus.

Therefore, according to the third embodiment, even though the cassetteis larger in size, the tape running areas S in the recording andreproducing apparatus will not be increased to a large extent. Thus,spaces near the tape running openings 92 can be effectively utilized,such as arranging additional members near the tape running openings 92.

The invention is not restricted to the above described embodiment, butcan be appropriately modified and improved based on the concept of theinvention. For example, although the above described embodiment has beendescribed referring to the M cassette and the L cassette, a similarstructure is applied to a cassette of an S size for a DVC. In addition,the invention is not restricted to the DVC, but can be applied to anytype of magnetic tape cassettes, provided that they may be such magnetictape cassettes as operable in the same recording and reproducingapparatus, but their recording and reproducing systems, size numbers,etc. are not limited.

Now a fourth embodiment of the invention will be described in detailreferring to FIGS. 6 and 7. FIG. 6 is a sectional view showing shapes ofmolds in the fourth embodiment of the invention. It is to be noted thatbecause structures of guide rollers and a magnetic tape cassette towhich the guide rollers are mounted are similar to the conventionalcase, their explanation will be omitted.

As shown in FIG. 6, a parting line PL1 between a pair of molds 260, 262for injection molding (260 is a movable mold, and 262 is a fixed mold)is positioned at a center of a guide roller 236 in a barrel-like shapewhich is a resin molded article, that is, the largest diameter portionof the guide roller, and the molds are formed in a shape of cavitiesdivided in halves at the center. In the cavities of both the molds 260,262, portions 264, 266 for forming a pin hole 236 a of the guide roller236 are projected in their respective center parts to be abutted againsteach other at a position of a parting line PL2. It goes without sayingthat the parting line PL2 is not limited to the position as shown in thedrawing, but can be appropriately changed, for example, to asubstantially center part (the same position as the line PL1) or so.

Accordingly, in a state where the molds 260, 262 are abutted againsteach other, molten resin which has been filled in the cavities throughrunners and gates formed in the molds 260, 262, although not shown, willbe molded into a shape of the cavities. After the resin has beenhardened, the movable mold 260 is released from the fixed mold 262, andthen, by thrusting a knock-out pin which is not shown, the guide roller236 molded in the barrel-like shape will be discharged to a position forstocking the products.

FIG. 7 shows the guide roller 236 which has been molded through theabove described injection molding process. The guide roller 236 has beenmolded substantially into a shape of a finished product having accuracyaccording to accuracy of the molds and abutting precision, except that amolding burr 236′ along the a foresaid parting line PL1 is projectedfrom the center part and another molding burr 236″ along the aforesaidparing line PL2 is projected from a tapered edge face at its one end.The first molding burr 236′ in a circumferential direction, and thesecond annular molding burr 236″ along the tapered edge will be cut in asubsequent cutting process, and then, the barrel shaped guide roller 236as the finished product will be obtained.

FIG. 8 is a sectional view showing shapes of molds according to a fifthembodiment of the invention. As shown in FIG. 8, a parting line PL1between a pair of molds 270, 272 for injection molding (270 is a movablemold, and 272 is a fixed mold) is positioned at both ends of a guideroller 236 which is a resin molded article, and the molds are formed ina shape of cavities divided in halves at both the ends. In respectivecenter parts of both the molds 270, 272, a pair of core molds 274, 276of a sideways extraction type for forming a pin hole 236 a of the guideroller 236 are arranged so as to be abutted against each other.

At a parting line PL2 between both the core molds 274, 276, one end ofthe pin hole 236 a is formed as a tapered edge. This allows the coremolds 274, 276 to be released without creating an undercut. However, itis needless to say that the parting line PL2 is not limited to theposition as shown in the drawing, but can be appropriately changed, forexample, to a substantially center part (the same position as the linePL1 in FIG. 6).

Accordingly, in a state where both the molds 270, 272 and the core molds274, 276 are abutted against each other, molten resin which has beenfilled in the cavities through runners and gates formed in the molds270, 272, although not shown, will be molded into a shape of thecavities. After the resin has been cooled, the movable mold 270 isreleased from the fixed mold 272 as indicated by an arrow, and byseparating the core molds 274, 276 from each other, the guide roller 236molded in a barrel-like shape can be obtained.

It is to be noted that the releasing process of the molds 270 to 274 maybe conducted in any order, provided that the molds do not interfere withone another in a direction of extraction.

FIG. 9 shows the guide roller 236 which has been molded through theabove described injection molding process. The guide roller 236 has beenmolded substantially into a shape of a finished product having accuracyaccording to accuracy of the molds and abutting precision, except that amolding burr 236′ along the aforesaid parting line PL1 is projectedalong a half divided position on an arc-shaped face and a half dividedposition on an end face, and a second circular molding burr 236″ isprojected along a tapered edge of one of the openings of the pin hole236 a.

Therefore, in a subsequent process, the molding burr 236′ will beremoved by applying a cutting edge along the arc-shaped face and bycutting, and the second annular molding burr 236″ will be also removedby an end face treatment.

Although there are more molding burrs formed in this fifth embodimentthan in the fourth embodiment, it is advantageous that precision testand shape modification can be performed at the same time in thesubsequent process, with a less cutting amount and in a shorter workingtime, as compared with the conventional case in which a molded articlein a shape of a straight cylinder has been machined into a barrel-likeshape.

The invention is not restricted to the above described embodiments, butappropriate modifications and improvements are possible. For example, itis apparent that an object of application of the invention is notlimited to a beta cam cassette, but any cassette having barrel shapedguide rollers formed of resin can be the object of the application.

INDUSTRIAL APPLICABILITY

As described herein above, in the magnetic tape cassettes according tothe invention, the positional restriction of the magnetic tape can beconducted in a stable manner while maintaining a certain tension even ina large cassette, because differences between the heights of theradially inner portions of the lower flanges and the heights of the ribsin the lower halves for restricting the height of the magnetic tapes areequal in a plurality of the magnetic tape cassettes which are equal invertical size and different in size in a horizontal direction.

Consequently, the magnetic tape will not be slackened, and damages ofthe tape edges can be prevented.

Moreover, according to the invention, because the tape running pathsconnecting the bosses around which the magnetic tapes are wound and theaforesaid guide members have the same inclinations, even in a pluralityof magnetic tape cassettes having different outer sizes, the taperunning areas in the recording and reproducing apparatus will not beenlarged to a large extent, even though the outer sizes are increased.

Further, according to the invention, because a pair of the tape runningopenings have the same width in a horizontal direction of the cassette,even in the plurality of the magnetic tape cassettes having differentouter sizes, the tape running areas in the recording and reproducingapparatus will not be enlarged to a large extent, even though the outersizes are increased.

Therefore, it will be possible to provide additional members near thetape running openings in the recording and reproducing apparatus, andthe recording and reproducing apparatus will not be upsized by providingthe members.

In the process for producing the guide roller in the magnetic tapecassette according to the invention, the parting line between the moldsfor injection molding is positioned at the largest diameter portion ofthe guide roller so as to mold it into a barrel-like shape, andthereafter, the molding burr projected from the parting line is removed,or the parting line between the molds for injection molding ispositioned at both ends of the guide roller so as to mold it into abarrel-like shape, and thereafter, the molding burr projected from theparting line is removed. Therefore, the guide roller can be directlymolded into the barrel-like shape by injection molding, with the simplesubsequent process, and can be manufactured at a low cost.

1. Magnetic tape cassettes in combination with a recording andreproducing apparatus which can commonly operate a plurality of sizes ofthe magnetic tape cassettes, the recording and reproducing apparatushaving common positioning pins for commonly positioning the plurality ofsizes of the magnetic tape cassettes inside the recording andreproducing apparatus, and each of the magnetic tape cassettescomprising: a magnetic tape for storing data; tape reels respectivelyprovided with bosses around which the magnetic tape is wound; upper andlower flanges for restricting vertical movement of the magnetic tape asit is wound around the tape reels, said lower flange having a radiallyinner portion; upper and lower halves for rotatably accommodating saidtape reels, said lower half respectively having ribs at a front end ofthe lower half, in such a manner that said magnetic tape is restrictedin height by said lower flange and the ribs; and positioning marksprovided in each of the magnetic tape cassettes for receiving the commonpositioning pins of the recording and reproducing apparatus, where adistance between the positioning marks are the same for each of themagnetic tape cassettes, wherein a size relationship among the magnetictape cassettes is such that each of the magnetic tape cassettes has asubstantially similar vertical length while a horizontal length variesamong each of the magnetic tape cassettes, and wherein a differencebetween a height of the radially inner portion and a height of the ribsis the same for each of the varying size magnetic tape cassettes;wherein at least one of the upper and lower halves having a pair ofguide members for defining a tape running area of tape running openings,and wherein: distances between the pair of guide members vary among eachof the magnetic tape cassettes, and inclinations defined by tape runningpaths that are defined by connecting the bosses and said guide members,are the same for each of the varying size magnetic tape cassettes. 2.The magnetic tape cassettes in combination with the recording andreproducing apparatus according to claim 1, wherein widths of the pairof tape running openings in a horizontal direction of said cassettes arethe same for each of the varying size magnetic tape cassettes, anddistances between the pair of guide members for restricting tape runningareas of said tape running openings at inner sides of the cassettes,vary among each of the magnetic tape cassettes.
 3. The magnetic tapecassettes in combination with the recording and reproducing apparatusaccording to claim 2, wherein the plurality of sizes of the magnetictape cassettes include at least two of S, M, L and LL cassettes.
 4. Themagnetic tape cassettes in combination with the recording andreproducing apparatus according to claim 1, wherein the plurality ofsizes of the magnetic tape cassettes include at least two of S, M, L andLL cassettes.
 5. Magnetic tape cassettes in combination with a recordingand reproducing apparatus which can commonly operate a plurality ofsizes of the magnetic tape cassettes, the recording and reproducingapparatus having common positioning pins for commonly positioning theplurality of sizes of the magnetic tape cassettes inside the recordingand reproducing apparatus, and each of the magnetic tape cassettescomprising: a magnetic tape for storing data; tape reels respectivelyprovided with bosses around which the magnetic tape is wound; upper andlower flanges for restricting vertical movement of the magnetic tape asit is wound around the tape reels; upper and lower halves for rotatablyaccommodating said tape reels, said upper and lower halves defining apair of tape running openings through which said magnetic tape runs, andat least one of the upper and lower halves having a pair of guidemembers for defining a tape running area of the tape running openings;and positioning marks provided in each of the magnetic tape cassettesfor receiving the common positioning pins of the recording andreproducing apparatus, wherein a size relationship among the magnetictape cassettes is such that horizontal lengths of each of the magnetictape cassettes vary among the magnetic tape cassettes, and whereindistances between the positioning marks are the same for each of thevarying size magnetic tape cassettes, distances between the pair ofguide members vary among each of the magnetic tape cassettes, andinclinations defined by tape running paths that are defined byconnecting the bosses and said guide members are the same for each ofthe varying size magnetic tape cassettes.
 6. Magnetic tape cassettes incombination with a recording and reproducing apparatus which cancommonly operate a plurality of sizes of the magnetic tape cassettes,the recording and reproducing apparatus having common positioning pinsfor commonly positioning the plurality of sizes of the magnetic tapecassettes inside the recording and reproducing apparatus, and each ofthe magnetic tape cassettes comprising: a magnetic tape for storingdata; tape reels respectively provided with bosses around which themagnetic tape is wound; upper and lower flanges for restricting verticalmovement of the magnetic tape as it is wound around the tape reels;upper and lower halves for rotatably accommodating said tape reels, saidupper and lower halves defining a pair of tape running openings throughwhich said magnetic tape runs, and at least one of the upper and lowerhalves having a pair of guide members for defining a tape running areaof the tape running openings; and positioning marks provided in each ofthe magnetic tape cassettes for receiving the common positioning pins ofthe recording and reproducing apparatus, wherein the horizontal lengthvaries among each of the magnetic tape cassettes, distances betweenpositioning marks are the same for each of the varying size magnetictape cassettes, widths of the pair of tape running openings in ahorizontal direction of said cassettes are the same for each of thevarying size magnetic tape cassettes, and distances between the pair ofguide members for restricting tape running areas of said tape runningopenings at inner sides of the cassettes vary among each of the magnetictape cassettes.
 7. Magnetic tape cassettes in combination with arecording and reproducing apparatus which can commonly operate aplurality of sizes of the magnetic tape cassettes, the recording andreproducing apparatus having common positioning pins for commonlypositioning the plurality of sizes of the magnetic tape cassettes insidethe recording and reproducing apparatus, and each of the magnetic tapecassettes comprising: a magnetic tape for storing data; tape reelsrespectively provided with bosses around which the magnetic tape iswound; upper and lower flanges for restricting vertical movement of themagnetic tape as it is wound around the tape reels, said lower flangehaving a radially inner portion; upper and lower halves for rotatablyaccommodating said tape reels, said lower half respectively having ribsat its front end in such a manner that said magnetic tape is restrictedin height by said lower flange and the ribs; and positioning marksprovided in a first one of the magnetic tape cassettes and at least oneadditional one of the magnetic tape cassettes for receiving the commonpositioning pins of the recording and reproducing apparatus, wheredistances between the positioning marks are the same for the firstmagnetic tape cassette and the at least one additional magnetic tapecassette, wherein a vertical height of the first magnetic tape cassetteis substantially equal to a vertical height of the at least oneadditional magnetic tape cassette, wherein a horizontal length of thefirst magnetic tape cassette is different than the horizontal length ofthe at least one additional magnetic tape cassette, and wherein adifference between a height of the radially inner portion of the firstmagnetic tape cassette and a height of a rib of the first magnetic tapecassette is substantially equal to a difference between a height of theradially inner portion of the at least one additional magnetic tapecassette and a height of a rib of the at least one additional magnetictape cassette; wherein at least one of the upper and lower halves have apair of guide members for defining a tape running area of tape runningopenings, and wherein: distances between the pair of guide members varyamong the first magnetic tape cassette and the at least one additionalmagnetic tape cassette, and inclinations defined by tape running pathsthat are defined by connecting the bosses and said guide members are thesame for the first magnetic tape cassette and the at least oneadditional magnetic tape cassette.
 8. The magnetic tape cassettes incombination with the recording and reproducing apparatus according toclaim 7, wherein: widths of the pair of tape running openings in ahorizontal direction of said magnetic tape cassettes are the same forthe first magnetic tape cassette and the at least one additionalmagnetic tape cassette, and distances between the pair of guide membersfor restricting tape running areas of said tape running openings atinner sides of the magnetic tape cassettes vary among the first magnetictape cassette and the at least one additional magnetic tape cassette. 9.The magnetic tape cassettes in combination with the recording andreproducing apparatus according to claim 8, wherein the plurality ofsizes of the magnetic tape cassettes include at least two of S, M, L andLL cassettes.
 10. The magnetic tape cassettes in combination with therecording and reproducing apparatus according to claim 7, wherein theplurality of sizes of the magnetic tape cassettes include at least twoof S, M, L and LL cassettes.
 11. Magnetic tape cassettes in combinationwith a recording and reproducing apparatus which can commonly operate aplurality of sizes of the magnetic tape cassettes, the recording andreproducing apparatus having common positioning pins for commonlypositioning the plurality of sizes of the magnetic tape cassettes insidethe recording and reproducing apparatus, and each of the magnetic tapecassettes comprising: a magnetic tape for storing data; tape reelsrespectively provided with bosses around which the magnetic tape iswound; upper and lower flanges for restricting vertical movement of themagnetic tape as it is wound around the tape reels; upper and lowerhalves for rotatably accommodating said tape reels, said upper and lowerhalves defining a pair of tape running openings through which saidmagnetic tape runs, and at least one of the upper and lower halveshaving a pair of guide members for defining a tape running area of thetape running openings; and positioning marks provided in a first one ofthe magnetic tape cassettes and at least one additional one of themagnetic tape cassettes for receiving the common positioning pins of therecording and reproducing apparatus, wherein a size relationship amongthe magnetic tape cassettes is such that horizontal lengths of the firstmagnetic tape cassette varies from the at least one additional magnetictape cassette, and wherein: distances between positioning marks are thesame for the first magnetic tape cassette and the at least oneadditional magnetic tape cassette, distances between the pair of guidemembers vary among the first magnetic tape cassette and the at least oneadditional magnetic tape cassette, and inclinations defined by taperunning paths that are defined by connecting the bosses and said guidemembers are the same for the first magnetic tape cassette and the atleast one additional magnetic tape cassette.
 12. Magnetic tape cassettesin combination with a recording and reproducing apparatus which cancommonly operate a plurality of sizes of the magnetic tape cassettes,the recording and reproducing apparatus having common positioning pinsfor commonly positioning the plurality of sizes of the magnetic tapecassettes inside the recording and reproducing apparatus, and each ofthe magnetic tape cassettes comprising: a magnetic tape for storingdata; tape reels respectively provided with bosses around which themagnetic tape is wound; upper and lower flanges for restricting verticalmovement of the magnetic tape as it is wound around the tape reels;upper and lower halves for rotatably accommodating said tape reels, saidupper and lower halves defining a pair of tape running openings throughwhich said magnetic tape runs, and at least one of the upper and lowerhalves having a pair of guide members for defining a tape running areaof the tape running openings; and positioning marks provided in a firstone of the magnetic tape cassettes and at least one additional one ofthe magnetic tape cassettes for receiving the common positioning pins ofthe recording and reproducing apparatus, wherein the horizontal lengthvaries among the first magnetic tape cassette and the at least oneadditional magnetic tape cassette, distances between positioning marksare the same for the first magnetic tape cassette and the at least oneadditional magnetic tape cassette, widths of the pair of tape runningopenings in a horizontal direction of said magnetic tape cassettes arethe same for the first magnetic tape cassette and the at least oneadditional magnetic tape cassette, and distances between the pair ofguide members for restricting tape running areas of said tape runningopenings at inner sides of the magnetic tape cassettes vary among thefirst magnetic tape cassette and the at least one additional magnetictape cassette.
 13. Magnetic tape cassettes in combination with arecording and reproducing apparatus which can commonly operate aplurality of sizes of the magnetic tape cassettes, the recording andreproducing apparatus having common positioning pins for commonlypositioning the plurality of sizes of the magnetic tape cassettes insidethe recording and reproducing apparatus, and each of the magnetic tapecassettes comprising: a magnetic tape for storing data; tape reelsrespectively provided with bosses around which the magnetic tape iswound; upper and lower flanges for restricting vertical movement of themagnetic tape as it is wound around the tape reels; and upper and lowerhalves for rotatably accommodating said tape reels, said upper and lowerhalves defining a pair of tape running openings through which saidmagnetic tape runs, and at least one of the upper and lower halveshaving a pair of guide members for defining a tape running area of thetape running openings; and positioning marks provided in a first one ofthe magnetic tape cassettes and at least one additional one of themagnetic tape cassettes for receiving the common positioning pins of therecording and reproducing apparatus, where distances between thepositioning marks are the same for the first magnetic tape cassette andthe at least one additional magnetic tape cassette, wherein thehorizontal length varies among the first magnetic tape cassette and theat least one additional magnetic tape cassette, widths of the pair oftape running openings in a horizontal direction of said magnetic tapecassettes are the same for each of the first magnetic tape cassette andthe at least one additional magnetic tape cassette, and distancesbetween the pair of guide members for restricting tape running areas ofsaid tape running openings at inner sides of the magnetic tape cassettesvary among the first magnetic tape cassette and the at least oneadditional magnetic tape cassette.